Methods for recovering machining scrap

ABSTRACT

A method including providing a quantity of metal, the quantity of metal being contaminated by a contaminant including a quantity of carbon; configuring a vacuum induction furnace to operate according to a set of operating parameters, the set of operating parameters being selected based on characteristics of the contaminant, the set of operating parameters including at least one of a pressure, an atmosphere composition, a pour temperature, or a hold time; charging the vacuum induction furnace with the quantity of metal; and operating the vacuum induction furnace to melt the quantity of metal in accordance with the set of operating parameters, whereby at least some of the contaminant is removed from the quantity of metal so as to provide an output metal having a concentration of carbon that is less than or equal to a concentration of carbon in the metal as cast.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent App. No. PCT/US2018/061928, filed Nov. 20, 2018, which claims the benefit of priority of U.S. Provisional Patent Application No. 62/588,752, filed Nov. 20, 2017, entitled “METHODS FOR RECOVERING ALUMINUM-LITHIUM SCRAP,” each of which are incorporated herein by reference in its entirety.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to methods for cleaning and recovering machining scrap, such aluminum-lithium (“AlLi”) alloy scrap, for reuse.

BACKGROUND OF THE PRIOR ART

When raw metal alloys (e.g., in the form of extrusions or plates) are to be machined to produce finished parts, they are coated with water-soluble lubricant to facilitate the machining process. In some embodiments, the water-soluble lubricant contains one or more organic compounds (i.e., compounds containing carbon) dissolved in water. The result of the machining process is a finished product and a quantity of scrap. In some cases, the finished product may use only about 10% of the raw material and the remainder of the raw material may become machining scrap, which remains contaminated with the water-soluble lubricant. The machining scrap has commercial value and is suitable for re-use, but cannot be re-used until the water-soluble lubricant has been cleaned therefrom.

SUMMARY OF THE INVENTION

In an embodiment, a method includes providing a quantity of metal, the quantity of metal being contaminated by a contaminant including a quantity of carbon; configuring a vacuum induction furnace to operate according to a set of operating parameters, the set of operating parameters being selected based on characteristics of the contaminant, the set of operating parameters including at least one of a pressure, an atmosphere composition, a pour temperature, or a hold time; charging the vacuum induction furnace with the quantity of metal; and operating the vacuum induction furnace to melt the quantity of metal in accordance with the set of operating parameters, whereby at least some of the contaminant is removed from the quantity of metal so as to provide an output metal having a concentration of carbon that is less than or equal to a concentration of carbon in the metal as cast.

In some embodiments, the quantity of metal includes a quantity of machining scrap. In some embodiments, a method also includes the step of prior to charging the vacuum induction furnace with the quantity of metal, compacting the quantity of metal into a unitary piece of metal.

In some embodiments, the set of operating parameters includes a hold time, and the hold time is between 0 minutes and 60 minutes. In some embodiments, the set of operating parameters includes a pressure, and the pressure is between 1 micron and 300 microns. In some embodiments, the set of operating parameters includes an atmosphere composition. In some embodiments, the atmosphere composition includes an inert gas atmosphere. In some embodiments, the set of operating parameters includes a pour temperature, and the pour temperature is between 700° C. and 770° C.

In some embodiments, the at least one contaminant includes sodium and a lubricant. In some embodiments, the set of operating parameters includes a pressure, a pour temperature, and a hold time, the pressure is between 1 micron and 300 microns, the temperature is between 700° C. and 755° C., and the hold time is between 30 minutes and 90 minutes.

In some embodiments, the quantity of metal includes one of a 2000-series aluminum alloy, a 5000-series aluminum alloy, a 6000-series aluminum alloy, a 7000-series aluminum alloy, or an 8000-series aluminum alloy. In some embodiments, the quantity of metal includes an aluminum-lithium alloy.

In some embodiments, the quantity of metal is further contaminated by a quantity of sodium. In some embodiments, the operating parameters include a temperature and a hold time, and the temperature and the hold time are selected so as to provide a residual sodium concentration that is less than a target concentration. In some embodiments, the target concentration is six parts per million.

In some embodiments, the contaminant includes a lubricant. In some embodiments, the operating parameters include a pour temperature of about 700° C. and substantially no hold time. In some embodiments, the operating parameters include a pressure of about 300 microns. In some embodiments, the operating parameters include an argon atmosphere and a pressure of about 1 atmosphere.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart describing the steps of a method according to an exemplary embodiment; and

FIG. 2 is a schematic illustration of a vacuum induction furnace that may be used in connection with an exemplary embodiment.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention can be further explained with reference to the included figures, wherein like structures are referred to by like numerals throughout the several views. The figures constitute a part of this specification and include illustrative embodiments of the present disclosure and illustrate various objects and features thereof. In addition, any measurements, specifications and the like shown in the figures are intended to be illustrative, and not restrictive. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. The figures shown are not necessarily to scale, with emphasis instead generally being placed upon illustrating the principles of the present invention. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

Among those benefits and improvements that have been disclosed, other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying figures. Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely illustrative of the invention that may be embodied in various forms. In addition, each of the examples given in connection with the various embodiments of the invention is intended to be illustrative, and not restrictive.

Throughout the specification and claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise. The phrases “in one embodiment” and “in some embodiments” as used herein do not necessarily refer to the same embodiment(s), though they may. Furthermore, the phrases “in another embodiment” and “in some other embodiments” as used herein do not necessarily refer to a different embodiment, although they may. Thus, as described below, various embodiments of the invention may be readily combined, without departing from the scope or spirit of the invention.

In addition, as used herein, the term “or” is an inclusive “or” operator, and is equivalent to the term “and/or,” unless the context clearly dictates otherwise. The term “based on” is not exclusive and allows for being based on additional factors not described, unless the context clearly dictates otherwise. In addition, throughout the specification, the meaning of “a,” “an,” and “the” include plural references, unless the context clearly dictates otherwise. The meaning of “in” includes “in” and “on”, unless the context clearly dictates otherwise.

In some embodiments, the exemplary invention relates to a method for recovering machining scrap such that it is suitable for re-use. In some embodiments, the exemplary invention relates to a method for melting, cleaning, and purifying machining scrap such that it is suitable for re-use. FIG. 1 shows a flowchart of a method 100 according to an exemplary embodiment. In step 110, a quantity of machining scrap is provided. In some embodiments, the machining scrap includes aluminum. In some embodiments, the machining scrap includes lithium. In some embodiments, the machining scrap includes aluminum and lithium. In some embodiments, the machining scrap includes a 2000-series aluminum alloy (i.e., a copper-based aluminum alloy). In some embodiments, the machining scrap includes a 7000-series aluminum alloy (i.e., a zinc-based aluminum alloy). In some embodiments, the machining scrap includes one or more of the alloys AA2050, AA2055, AA2060, AA2090, AA2091, AA2094, AA2095, AA2097, AA2098, AA2099, AA2195, AA2196, AA2197, AA2198, AA2199, AA2297 and AA2397, as these alloys are by the Aluminum Association. In some embodiments, the machining scrap is coated with a lubricant. In some embodiments, the lubricant includes sodium. In some embodiments, the machining scrap is not coated with a lubricant. In some embodiments, the machining scrap includes a non-lithium-containing aluminum alloy. In some embodiments, the machining scrap has a bulk density of between 20 and 50 pounds per cubic foot.

In step 120, at least a portion the machining scrap is compressed into a unitary piece. In some embodiments, the piece is of the type commonly referred to as a “puck”. In some embodiments, the machining scrap is bailed. In some embodiments, the machining scrap includes solids. In some embodiments, the piece has a mass of about 80 kilograms. In some embodiments, the piece has a weight of about 1,500 pounds. In some embodiments, the piece has a weight of between 3,000 pounds and 6,000 pounds. In some embodiments, a quantity of the machining scrap (e.g., in quantities as noted above) is selected for further processing, but is not compressed into a piece. In some embodiments, a puck is broken into smaller pieces before further processing occurs. In some embodiments, omitting the step of forming pucks, or, alternately, breaking the pucks into smaller pieces, will provide an increased lubricant-coated surface area that is exposed during subsequent steps of the method 100. It will be apparent to those of skill in the art that this step may be repeated as necessary based on the amount of the machining scrap provided in step 110.

In step 130, a vacuum induction furnace is provided. In some embodiments, the vacuum induction furnace is a vacuum induction degassing and pouring furnace. FIG. 2 shows an exemplary vacuum induction furnace. In some embodiments, the vacuum induction furnace includes an enclosed vacuum chamber. In some embodiments the vacuum induction furnace includes a vacuum pump that is configured to remove gases (e.g., air, argon, vaporized lubricant) from the vacuum chamber. In some embodiments, the vacuum pump is configured to provide a configurable level of pressure within the vacuum chamber. In some embodiments, the vacuum pump is configured to provide a level of pressure between 1 micron (i.e., a unit of pressure that is equal to 1/1000 of a millimeter of mercury) and 1 atmosphere within the vacuum chamber. In some embodiments, the vacuum induction furnace includes a supply of argon that is configured to selectively introduce argon into the vacuum chamber. In some embodiments, the vacuum induction chamber includes a vent. In some embodiments, the vacuum induction furnace includes an induction furnace within the vacuum chamber. In some embodiments, the induction furnace is configured to heat the contents of a vessel to a selected temperature and for a selected period of time. In some embodiments, the vacuum induction furnace includes a mold within the vacuum chamber. In some embodiments, the vacuum induction furnace is configured to be operable to pour contents of the vessel (e.g., melted machining scrap) into the mold at a selected time (e.g., after the contents have been heated for a selected period of time).

Referring back to FIG. 1, in step 140, the vacuum induction furnace is configured to operate according to a given set of parameters. In some embodiments, the parameters are selected so as to clean, melt, and cast aluminum-lithium machining scrap while minimizing oxidation losses, maximizing alloy retention (particularly maximizing retention of lithium), remove contaminants (e.g., lubricant) if necessary, and minimizing cycle time. In some embodiments, the parameters include a target temperature. In some embodiments, the parameters include a rate of heating to arrive at the target temperature. In some embodiments, heating is performed at a controlled rate so as to ensure that no moisture is trapped below the level of the melted metal. In some embodiments, the parameters are selected based on the characteristics of the machining scrap. In some embodiments, the parameters are selected based on whether the machining scrap is coated with lubricant. In some embodiments, the parameters are selected based on whether the machining scrap includes contaminants (e.g., sodium, calcium, potassium, etc.). In some embodiments, the vacuum induction furnace is configured to provide a vacuum. In some embodiments, the vacuum induction furnace is configured to provide an argon atmosphere. In some embodiments in which the vacuum induction furnace is to be configured to melt scrap having no lubricant (e.g., scrap resulting from dry machining), the vacuum induction furnace is configured to provide an argon atmosphere at or about atmospheric pressure, to provide a temperature of about 730° C., and to provide no hold time once the temperature has been reached. In some embodiments in which the vacuum induction furnace is to be configured to melt scrap having lubricant but no contamination (e.g., sodium, calcium, potassium, etc.), the vacuum induction furnace is configured to provide either (a) a vacuum of about 300 microns or (b) an argon atmosphere at or about atmospheric pressure, to provide a temperature of about 700° C., and to provide no hold time once the temperature has been reached. In some embodiments in which the vacuum induction furnace is to be configured to melt scrap having lubricant and contamination (e.g., sodium, calcium, potassium, etc.), the vacuum induction furnace is configured to provide a vacuum of about 300 microns, to provide a temperature of between about 700° C. and about 755° C., and to provide a hold time of one hour. It will be apparent to those of skill in the art that the above configurations are only exemplary and that other optimized configurations may be determined based on the characteristics of a specific batch of machining scrap at hand, based on general characteristics of an ongoing stream of machining scrap, etc.

Continuing to describe step 140 of the exemplary method 100, the following will describe ranges of values for various parameters of the vacuum induction furnace. It will be apparent to those of skill in the art that all of the ranges described herein are inclusive (i.e., a range of between 100° C. and 200° C. includes the values of 100° C. and 200° C. as well as all values therebetween). In some embodiments, the parameters include an internal atmosphere of the vacuum induction furnace (e.g., an atmosphere within the vacuum chamber of the vacuum induction furnace). In some embodiments, the internal atmosphere includes a pressure level. In some embodiments, the pressure level is represented in microns. In some embodiments, the pressure level is 1 micron. In some embodiments, the pressure level is 100 microns. In some embodiments, the pressure level is 200 microns. In some embodiments, the pressure level is 300 microns. In some embodiments, the pressure level is between 1 micron and 100 microns. In some embodiments, the vacuum level is between 1 micron and 200 microns. In some embodiments, the pressure level is between 1 micron and 300 microns. In some embodiments, the pressure level is between 100 microns and 200 microns. In some embodiments, the pressure level is between 100 microns and 300 microns. In some embodiments, the pressure level is between 200 microns and 300 microns. In some embodiments, the pressure level is represented in millibars. In some embodiments, the pressure level is 0.001 millibars. In some embodiments, the pressure level is 0.132 millibars. In some embodiments, the pressure level is 0.263 millibars. In some embodiments, the pressure level is 0.4 millibars. In some embodiments, the pressure level is between 0.001 millibars and 0.132 millibars. In some embodiments, the pressure level is between 0.001 millibars and 0.263 millibars. In some embodiments, the pressure level is between 0.001 millibars and 0.4 millibars. In some embodiments, the pressure level is between 0.132 millibars and 0.263 millibars. In some embodiments, the pressure level is between 0.132 millibars and 0.4 millibars. In some embodiments, the pressure level is between 0.263 millibars and 0.4 millibars. In some embodiments, the pressure level is about 1,000 microns. In some embodiments, the pressure level is between 900 microns and 1,000 microns. In some embodiments, the pressure level is about 1 atmosphere. In some embodiments, the internal atmosphere includes an inert gas atmosphere. In some embodiments, the internal atmosphere includes an argon atmosphere. In some embodiments, the vacuum induction furnace is configured to generate a vacuum (e.g., a vacuum of 100 microns) and then to fill the internal atmosphere with argon. In some embodiments, the vacuum induction furnace is configured to generate a vacuum (e.g., a vacuum of 100 microns) and then to fill the internal atmosphere with argon at a pressure level of about 1 atmosphere.

Continuing to describe step 140 of the exemplary method 100, in some embodiments, the parameters include a pour temperature. In some embodiments, the pour temperature is 700° C. In some embodiments, the pour temperature is 710° C. In some embodiments, the pour temperature is 720° C. In some embodiments, the pour temperature is 730° C. In some embodiments, the pour temperature is 740° C. In some embodiments, the pour temperature is 750° C. In some embodiments, the pour temperature is 755° C. In some embodiments, the pour temperature is 760° C. In some embodiments, the pour temperature is 768° C. In some embodiments, the pour temperature is 770° C. In some embodiments, the pour temperature is between 700° C. and 710° C. In some embodiments, the pour temperature is between 700° C. and 720° C. In some embodiments, the pour temperature is between 700° C. and 730° C. In some embodiments, the pour temperature is between 700° C. and 740° C. In some embodiments, the pour temperature is between 700° C. and 750° C. In some embodiments, the pour temperature is between 700° C. and 760° C. In some embodiments, the pour temperature is between 700° C. and 770° C. In some embodiments, the pour temperature is between 710° C. and 720° C. In some embodiments, the pour temperature is between 710° C. and 730° C. In some embodiments, the pour temperature is between 710° C. and 740° C. In some embodiments, the pour temperature is between 710° C. and 750° C. In some embodiments, the pour temperature is between 710° C. and 760° C. In some embodiments, the pour temperature is between 710° C. and 770° C. In some embodiments, the pour temperature is between 720° C. and 730° C. In some embodiments, the pour temperature is between 720° C. and 740° C. In some embodiments, the pour temperature is between 720° C. and 750° C. In some embodiments, the pour temperature is between 720° C. and 760° C. In some embodiments, the pour temperature is between 720° C. and 770° C. In some embodiments, the pour temperature is between 730° C. and 740° C. In some embodiments, the pour temperature is between 730° C. and 750° C. In some embodiments, the pour temperature is between 730° C. and 760° C. In some embodiments, the pour temperature is between 730° C. and 770° C. In some embodiments, the pour temperature is between 740° C. and 750° C. In some embodiments, the pour temperature is between 740° C. and 760° C. In some embodiments, the pour temperature is between 740° C. and 770° C. In some embodiments, the pour temperature is between 750° C. and 760° C. In some embodiments, the pour temperature is between 750° C. and 770° C. In some embodiments, the pour temperature is between 760° C. and 770° C.

Continuing to describe step 140 of the exemplary method 100, in some embodiments, the parameters include a hold time (i.e., a time period during which a charge received in the vacuum induction furnace is held at a target temperature and pressure once the target temperature and pressure have been reached). In some embodiments, the hold time is 0 minutes. In some embodiments, the hold time is 30 minutes. In some embodiments, the hold time is 60 minutes. In some embodiments, the hold time is 90 minutes. In some embodiments, the hold time is between 0 minutes and 30 minutes. In some embodiments, the hold time is between 30 minutes and 60 minutes. In some embodiments, the hold time is between 60 minutes and 90 minutes. In some embodiments, the hold time is between 0 minutes and 60 minutes. In some embodiments, the hold time is between 30 minutes and 90 minutes. In some embodiments, the hold time is between 0 minutes and 90 minutes.

Continuing to refer to FIG. 1, in step 150, the piece formed from the machining scrap in step 120 is placed within the vacuum induction furnace. In step 160, the vacuum induction furnace is operated to heat the machining scrap. In some embodiments, heating is performed as configured in step 140. During the heating process under the selected conditions, lubricants are removed from the machining scrap. In some embodiments, lubricants are vaporized and are carried away from the machining scrap in the vacuum stream. In some embodiments, the lubricants are collected from the vacuum stream for subsequent use and/or disposal. In some embodiments, small amounts of the lubricants condense on the inside surface of the vacuum chamber. In some embodiments, lubricants are vaporized and oxidized.

In some embodiments, the heating step includes heating to vaporize lubricants. In some embodiments, the step of heating to vaporize lubricants includes holding the machining scrap at a selected temperature and in a selected environmental composition for a time that is sufficient to vaporize the lubricants. In some embodiments, the time is about one hour. In some embodiments, the selected environment is a medium vacuum pressure (e.g., between 0.001 millibars and 30 millibars) and the temperature is a temperature that is greater than the boiling point of the lubricants at the selected pressure, but less than the solidus point of the machining scrap (e.g., about 660° C.). In some embodiments, the temperature is less than the boiling point of the lubricants at standard temperature and pressure (which is, for example, 370° C.).

In some embodiments, the environment is an argon environment at about one atmosphere and the temperature is a temperature that is greater than the boiling point of the lubricants (which is, for example, 370° C. at standard temperature and pressure), but less than the solidus point of the machining scrap (e.g., about 660° C.).

In some embodiments, the heating step includes heating to vaporize and oxidize lubricants. In some embodiments, the step of heating to vaporize and oxidize lubricants includes holding the machining scrap at a selected temperature and in a selected environmental composition for a time that is sufficient to vaporize the lubricants. In some embodiments, the time is about one hour. In some embodiments, the selected environment is a low vacuum pressure (e.g., between 30 millibars and 1000 millibars) and air environment and the temperature is a temperature that is greater than the boiling point of the lubricants at the selected pressure, but less than the solidus point of the machining scrap (e.g., about 660° C.). In some embodiments, the temperature is less than the boiling point of the lubricants at standard temperature and pressure (which is, for example, 370° C.).

In some embodiments, the environment is an argon/air environment. In some embodiments, the argon/air environment includes between 0% and 100% argon and the balance air. In some embodiments, the temperature is a temperature that is greater than the boiling point of the lubricants (which is, for example, 370° C. at standard temperature and pressure), but less than the solidus point of the machining scrap (e.g., about 660° C.).

In some embodiments, the environment is an air environment at or about atmospheric pressure and the temperature is a temperature that is greater than the boiling point of the lubricants (which is, for example, 370° C. at standard temperature and pressure), but less than the solidus point of the machining scrap (e.g., about 660° C.).

Continuing to refer to FIG. 1, in step 170, the vacuum induction furnace is operated to melt the machining scrap. In some embodiments, this step includes maintaining atmospheric conditions (e.g., pressure, atmospheric composition) that were used in step 160. In some embodiments, this step includes changing atmospheric conditions. In some embodiments, this step includes continuing to heat the machining scrap (e.g., from a temperature at which lubricant is vaporized and/or oxidized, as discussed above with reference to step 160) until the machining scrap reaches its solidus point.

In some embodiments, the melting step includes melting so as to vaporize and/or oxidize lubricant during the melting step. In some embodiments, the step of melting so as to vaporize and/or oxidize lubricant includes melting at a predefined environmental composition. In some embodiments, the environment is a low vacuum (e.g., between 30 millibars and 1000 millibars) and air environment and the temperature is a temperature at or above the solidus point of the machining scrap (e.g., about 660° C.). In some embodiments, the environment is an argon/air environment at a pressure of at or about atmospheric pressure and the temperature is a temperature at or above the solidus point of the machining scrap (e.g., about 660° C.). In some embodiments, the environment is an air environment at a pressure of at or about atmospheric pressure and the temperature is a temperature at or above the solidus point of the machining scrap (e.g., about 660° C.).

Continuing to refer to FIG. 1, in step 180, after the machining scrap is completely liquid, the temperature is raised to the level selected during step 140, and is held at this prescribed level for the prescribed hold time. While the melted scrap is being held at this temperature, any contaminants (e.g., sodium, calcium, potassium, etc.) are vaporized and carried away from the melted scrap in the vacuum stream. In some embodiments, the contaminants, if any, are collected from the vacuum stream for subsequent use and/or disposal.

Continuing to refer to FIG. 1, in step 190, the melted machining scrap is poured as needed (e.g., cast into a mold, fed into an ingot caster, etc.). It will be apparent to those of skill in the art that steps 150 through 190 may be repeated as necessary based on the amount of machining scrap at hand. Following step 190, the method 100 is complete.

In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above has been cleaned of substantially all lubricant that was originally coated thereon. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes substantially no residual carbon. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace includes 200 parts per million or less of residual carbon. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace includes 190 parts per million or less of residual carbon. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace includes 180 parts per million or less of residual carbon. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace includes 170 parts per million or less of residual carbon. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace includes 160 parts per million or less of residual carbon. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace includes 150 parts per million or less of residual carbon. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace includes 140 parts per million or less of residual carbon. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace includes 130 parts per million or less of residual carbon. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace includes 120 parts per million or less of residual carbon. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace includes 110 parts per million or less of residual carbon. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace includes 100 parts per million or less of residual carbon. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace includes an amount of residual carbon that is equal to or less than an amount of residual carbon in an as-cast aluminum alloy.

In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes substantially no residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 25 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 24 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 23 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 22 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 21 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 20 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 19 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 18 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 17 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 16 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 15 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 14 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 13 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 12 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 11 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 10 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 9 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 8 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 7 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 6 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 5 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 4 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 3 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 2 parts per million or less of residual sodium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace as described above includes 1 parts per million or less of residual sodium.

In some embodiments, the process described above is performed in the absence of flux (i.e., is flux-free). In some embodiments, the material that is yielded by the operation of the vacuum induction furnace retains substantially all lithium that was contained therein. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace retains substantially all alloy material that was contained therein prior to melting in the vacuum induction furnace. In some embodiments, little or no oxidation occurs.

In some embodiments, the material that is yielded by the operation of the vacuum induction furnace includes between 0% and 0.4% lithium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace includes between 0.4% and 0.8% lithium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace includes between 0.8% and 1.2% lithium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace includes between 1.2% and 1.6% lithium.

In some embodiments, the material that is yielded by the operation of the vacuum induction furnace includes between 1.6% and 2.0% lithium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace includes between 2.0% lithium and 2.4% lithium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace includes between 2.4% lithium and 2.7% lithium. In some embodiments, the material that is yielded by the operation of the vacuum induction furnace is suitable for repeated commercial use.

The exemplary embodiments described herein have been described with specific reference to techniques for melting and cleaning AlLi machining scrap that is contaminated with sodium and/or lubricant. However, it will be apparent to those of skill in the art that the principles embodied by the exemplary embodiments are equally applicable to the melting and cleaning of any other metal. It will be further apparent to those of skill in the art that the principles embodied by the exemplary embodiments are equally applicable to metals contaminated by any other type of high vapor pressure contaminant.

While a number of embodiments of the present invention have been described, it is understood that these embodiments are illustrative only, and not restrictive, and that many modifications may become apparent to those of ordinary skill in the art. Further still, unless the context clearly requires otherwise, the various steps may be carried out in any desired order, and any applicable steps may be added and/or eliminated. 

We claim:
 1. A method, comprising: charging a furnace with the quantity of metal, the quantity of metal comprising a carbon-containing contaminant; configuring the furnace to operate according to a set of operating parameters, the set of operating parameters being selected based on characteristics of the carbon-containing contaminant, the set of operating parameters including at least one of a pressure, an atmosphere composition, a pour temperature, and a hold time; operating the furnace to melt the quantity of metal in accordance with the set of operating parameters, whereby at least some of the carbon-containing contaminant is removed from the quantity of metal; discharging an output metal, wherein a concentration of carbon in the output metal is less than a concentration of carbon in the quantity of metal.
 2. The method of claim 1, wherein the quantity of metal includes a quantity of machining scrap.
 3. The method of claim 1, further comprising the step of: prior to charging the furnace with the quantity of metal, compacting the quantity of metal into a unitary piece of metal.
 4. The method of claim 1, wherein the set of operating parameters includes a hold time, and wherein the hold time is between 0 minutes and 60 minutes.
 5. The method of claim 1, wherein the set of operating parameters includes a pressure, and wherein the pressure is between 1 micron and 300 microns, wherein 1 micron of pressure is equal to 1/1000th of a millimeter of mercury.
 6. The method of claim 1, wherein the set of operating parameters includes an atmosphere composition.
 7. The method of claim 6, wherein the atmosphere composition includes an inert gas atmosphere.
 8. The method of claim 1, wherein the set of operating parameters includes a pour temperature, and wherein the pour temperature is between 700° C. and 770° C.
 9. The method of claim 1, wherein the quantity of metal comprises sodium.
 10. The method of claim 9, wherein the set of operating parameters includes a pressure, a pour temperature, and a hold time, wherein the pressure is between 1 micron and 300 microns, wherein the temperature is between 700° C. and 755° C., and wherein the hold time is between 30 minutes and 90 minutes.
 11. The method of claim 9, wherein the operating parameters include a temperature and a hold time, and wherein the temperature and the hold time are selected so as to provide a residual sodium concentration that is less than a target concentration.
 12. The method of claim 11, wherein the target concentration is six parts per million.
 13. The method of claim 1, wherein the carbon-containing contaminant is an organic compound.
 14. The method of claim 13, wherein the operating parameters include a pour temperature of about 700° C. and substantially no hold time.
 15. The method of claim 14, wherein the operating parameters include a pressure of about 300 microns.
 16. The method of claim 15, wherein the operating parameters include an argon atmosphere and a pressure of about 1 atmosphere.
 17. The method of claim 1, wherein the quantity of metal is aluminum alloy scrap.
 18. The method of claim 17, wherein the aluminum alloy scrap is scrap of one of a 2000-series aluminum alloy, a 5000-series aluminum alloy, a 6000-series aluminum alloy, a 7000-series aluminum alloy, or an 8000-series aluminum alloy.
 19. The method of claim 17, wherein the aluminum alloy scrap is scrap of an aluminum-lithium alloy.
 20. A method comprising: charging a furnace with 2000-series aluminum alloy scrap, the 2000-series aluminum alloy scrap comprising lithium and an organic contaminant; configuring the furnace to operate according to a set of operating parameters, the set of operating parameters being selected based on characteristics of the organic contaminant, the set of operating parameters including at least one of a pressure, an atmosphere composition, a pour temperature, and a hold time; operating the furnace to melt the 2000-series aluminum alloy scrap in accordance with the set of operating parameters, whereby at least some of the organic contaminant is removed from the quantity of metal; discharging a purified 2000-series aluminum alloy material, the discharged 2000-series aluminum alloy material comprising the lithium. 